Signaling system in telephone plants with central battery.



No. 780,713. E PATENTED JAN. 24, 1905.

, x A. EKSTEUM. SIGNALING SYSTEM IN TELEPHONE PLANTS WITH CENTRAL BATTERY.

APPLIGA TION FILED 00T- 20,1902.

I71 U6 77/ 550 r.

UNITED STATES Patented January 24, 1905.

PATENT OFFICE.

ALFRED EKsTEoM, or STOOKHOLM, SWEDEN, ASSIGNOR TO AKTIEBO- LAGET L. M. ERIOSSON & 00., OF STOCKHOLM, SWEDEN.

SIGNALING-SYSTEM IN TELEPHONE PLANTS WITH CENTRAL BATTERY.

SPECIFICATION forming part of Letters Patent No. 780,713, dated January 24;, 1905. Application filed October 20, 1902. Serial No. 127,958.

To (MZ whom 2 25 may concern: I 7

Be it known that I, ALFRED EKsTRoM, doctor of philosophy, a subject of the King of Sweden and Norway, and a resident of Tegnersgatan 4:, Stockholm, in the Kingdom of Sweden, have invented a certain new and useful Improved Signaling System in Telephone Plants with Central Battery, of which the following is a specification, reference being had therein to the accompanying drawing.

This invention relates to improvements in telephone exchange systems of that kind where the voice-currents are supplied by a battery placed at the central station, said battery being common to all lines.

More especially the invention relates to that class of central-battery systems where a relay inserted in the line controls the calling as also the clearing-out signal, said relay being here inafter called the line-relay.

Further characterized, the invention relates to improvements in telephone-exchange systems of the kind specified for producing the calling and the clearing-out signal, as also for instantaneously signifying lines already in use to be busied.

The characterizing feature of the invention consists in that the linerelay-when being eX- cited-o'. e. when the subscriber calls the station by removing his hand-microphone from its switch-hookcloscs a circuit through the calling-signal, said circuit being opened as soon as the operator inserts a plug in a springjack connected with the calling-line, by which operation the clearing-out signal placed in the third conductor of the cord is simultaneously short-circuited through the armature of the line-relay. This short circuit, that is closed throughout the whole conversation,pre- Vents the clearing-out signal from being active. When, however, the conversation is completed and the subscriber places his handmicrophone in its switch-hook, the armature of the line-relay will again take up its normal position and open the short circuit about the clearing-out signal, whereby the said signal becomes active and signifies that the lines connected together are to be disconnected.

At the same time as the line-relay is excited one pole of the test-battery is connected with the test-conductor of the line, so that the line ularly described.

A is the substation. When the lever or switch-hook It takes up its lower positionz'. 0., when the hand-microphone hangs in its hookthe signal-bell 6 and the condenser are included in the line. When, on the contrary, the hand-microphone is removed and the lever or switch-hook it is in its upper po sition, the microphone z. and the receiver or telephone r are in the line, the signal-bell 6 being then connected in parallel with the mi crophone t; In order to avoid any detrimental action upon the transmitting of the voicecurrents, the signal-bell has a great resistance.

1 and 2 are the two branches of the line drawn from the substation to the exchangeofiice or central station. In the central station the line is connected partly through conductors 3 4 with the multiple jacks J J &c., and partly with the answering-jack J, as also with the inductive resistance R R the latter being connected at their othervsides with the central battery 0. One resistance R is constructed as a relay and is hereinafter called the line-relay. R is another relay, hereinafter called the cut-off relay, said relay being connected with the armature of the linerelay and provided with two windings arranged in such a manner that a current flowing through the two windings in series does not actuate the armature 2 1 of the cut-off relay. The junction of the two windings is connected with the test-springs of the linejacks.

S is the calling-signal.

P and P are two plugs connected by aeord having three conductors. Interposed in the conductors corresponding to the branches of the line are condensers K K The third conductor, whose middle point is connected with the battery B, includes the clearing-out signals S S one for each plug. The battery B supplies the current for the signals and for the testing.

The operationof the system described is the following: When the hand-microphone hangs in its switch-hook at substation A, the condenser is is included in the line and provides a break for the continuous current from the central battery C. When, however, the subscriber calls the station by removing his hand-microphone from its switch-hook, a circuit is closed from the battery C through conductors 5 and 6, relay R conductor 7, branch 2 of the line, receiver 1*, signal-bell b, and microphone tin parallel, branch 1 of the line,

conductor 8, resistance R, and conductors 9 and 10 back to the battery C. The relay R will thus be energized and attract its armature 23, by which the following circuit is established: earth conductor 11, battery B,

conductors 12 13, armature 23, conductor 14:, armature 24, conductor 15, calling-signal S, and earth conductor 16. The lamp S will then glow and announce the calling. Ashuntcircuit is also closed through the wire 14:, both windings of the cut-off relay R and earth conductor 19. The two windings of the cutoff relay counteract each other, and the armature 24 is therefore not attracted. The junction of the two windings being, however, connected through conductor 18 with the test springs of the jacks, the thimbles'or test-rings of the jacks appertaining to the line are supplied with current. The moment the subscriber calls the station his line is thus signified to be busied. The operator when inserting a plug in the answering-jack J establishes the following circuit: earth conductor 11, battery B, conductors 20 21, lamp S conductor 22, third conductor of plug P, thimble and test-spring of jack J, conductor 18, one winding of the cut-off relay R and earth conductor 19. This causes the armature 24 to be attracted and held in its attracted position as long as the plug remains in the jack. The attraction of armature 24, however, creates a short circuit about the signal-lamp S through wires 12 and 13, armature 23, conductor 14:, and armature 24, so that only a weak current will pass through lamp S and the latter will not glow. The short circuit about the clearing-out signal-lamp is, however, dependent on the position of armature 23 of the line-relay R Thelatter being controlled directly from the apparatus at the substation, it is obvious that when the subscriber after having finished his conversation places the handmicrophone in the switch hook (whereby the condenser Z2 establishes a break for the continuous current from battery C through the line and the relay R releases its armature 23, which falls back in its normal position) the short circuit about the clearingout-signal lamp S is broken. The whole current from battery B will then pass through lamp S which is illuminated, and announces the conversation to be finished. As soon as the operator removes the plug from the jack the circuit through the clearing-out-signal lamp is broken, and the lamp goes out.

The part of the operation relating to the cord for the plug P 2I. 0., the method of connecting the calling subscriber with the required numberhas not been particularly described, said method not differing in any way from that generally employed.

In the drawings the calling-signals, as also the clearing-out signals, have been illustrated in the form of lamps; but it is obvious that any other suitable signals might be used.

Having now described my invention, what I claim as new, and desire to secure by Letters Patent, is-

1. In a central-battery telephone system, a line-relay R excited during the whole time the telephone-receiver is removed from its switch-hook, a cut-0t? relay R actuated when a plug P is inserted in the subscribers jack, a calling-signal S, means controlled by the cut-off relay for cutting out the callingsignal S when the plug is inserted, a clearingout signal S means controlled by the cut-oli' relay for establishing a short circuit about the clearing-out signal S when the plug is inserted, and means controlled by the liuerelay for breaking the said short circuit when the line-relay becomes inactive on account of the telephone-receiver being replaced upon its hook, substantially as described.

2. In a central-battery telephone system, a line-relay R excited during the whole time the telephone-receiver is removed from its switch-hook, a cut-off relay R having two windings the junction of which is connected with the test-conductor 18 of the line, said relay R being inactive for currents through both windings in series, whereas it is actuated by a current through one winding, means for supplying both windings of the cut-off relay with current in series, when the line-relay is operated, whereby the test-conductor is supplied with current and marks the line busy by the subscribers calling of the exchange, means for supplying the one winding of the cut-off relay with current, when a plug P is inserted in the subscribers jack, a calling signal S, means controlled by the cut-01f relay for cutting out the calling-signal S when the plug is inserted, a clearing-out signal S, means controlled by the cut-off relay for establishing a short circuit about the clearing- IIO ' out signal S when the plug is inserted, and my name in the presence of two subscribing means controlled by the line-relay'for break- Witnesses. ing the said short circuit When the line-relay becomes inactive on account of the telephone- 5 receiver being replaced upon its hook, sub- Witnesses:

stantially as described. ERNsT SVANeVIsT,

In Witness whereof I have hereunto signed AUG. SoRENsoN.

I ALFRED EKSTRQM. 

